A second worker exposed to dangerously high levels of radiation during Japan's worst nuclear accident last September died yesterday morning at a hospital in Tokyo.

Masato Shinohara, 40, died of multiple organ failure, doctors said. He had been connected to a respirator since February, after his condition worsened.

Mr Shinohara was one of two employees of the nuclear fuel company JCO exposed to massive levels of radiation during the accident on September 30 at the firm's uranium processing plant in Tokaimura, 80 miles north-east of Tokyo. Mr Shinohara and Hisashi Ouchi set off an uncontrolled chain reaction after mistakenly pouring too much uranium into a processing tank.

Mr Ouchi, 35, died last December, becoming the first fatality in Japan's civil nuclear power programme. A third worker, Yutaka Yokokawa, who was in an adjacent room when the accident occurred, was released from hospital the same month.

Yoshiro Mori, the prime minister, described Mr Shinohara's death as "extremely regrettable", and vowed to continue tightening up safety at Japan's nuclear power facilities. Hirofumi Nakasone, head of the science and technology agency, visited the hospital yesterday morning to offer the government's condolences to Mr Shinohara's family.

Doctors at Tokyo University Hospital, where Mr Shinohara had been treated since April 10, paid tribute to his courage. Kazuhiko Maekawa, head of the hospital's intensive care unit, said treating Mr Shinohara had made him aware of the limitations of medical science. "I was overwhelmed by a sense of helplessness in the face of something caused by human arrogance," he said.

At one point, Mr Shinohara's condition had shown signs of improvement. He received a blood transfusion in October, and on New Year's Day was well enough to venture into the garden at Tokyo University's institute of medical science in his wheelchair. In late February, however, doctors placed him on a respirator when pneumonia and radiation damage to his respiratory system brought on severe breathing difficulties.

Mr Shinohara, was married, with three children. He joined JCO's predecessor in 1984. Two years ago, he was placed in charge of processing nuclear fuel for the Joyo fast-breeder nuclear reactor not far from the Tokaimura plant.

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